This invention relates to internal combustion engine idle speed control methods systems and more particularly to methods and systems for estimating engine load in controlling idle speed.
As is known in the art, engine idle operation involves providing enough power output from the engine to compensate for engine friction and pumping losses, and to counteract front-end accessory and transmission loading. Too much power will cause an annoying flare in engine speed, and too little power will result in a dip in engine speed which may destabilize engine operation or even cause the engine to stall. Idle speed control strategies consist of one or a combination of:
i. feed-forward control to estimate the magnitude of the engine losses and loading based on environmental conditions (e.g., ambient temperature, engine coolant temperature, transmission state, and air-conditioning and power-steering conditions); and
ii. feedback control to correct engine speed errors which result from unanticipated loads and errors in the feed-forward estimations.
The feed-forward control typically relies on a model of each individual engine loss or load to calculate the resulting impact on the engine. The inventor has recognized that these models can be quite complex and require calibration for a number of tables or parameters which describe the physics involved. Further, the inventors have recognized that this model-based approach is limited by the sensor""s ability to detect the variables affecting the presence, magnitude and timing of a given load, and it is incapable of compensating for a load which is unanticipated.
In accordance with the present invention, a method is provided for generating an idle control signal for an internal combustion engine. The method includes: estimating engine combustion torque; and generating the idle control signal as a function of the estimated combustion torque and engine speed, n.
In accordance of one feature of the invention, a method is provided for generating an idle control signal for an internal combustion engine. The method includes: estimating combustion torque xcfx84ind; and producing the idle control signal for the engine as a function of the difference between: (A) a time rate of change in engine rotational speed, dn/dt, and; (B) the sum of the estimated combustion generated torque xcfx84ind and a function of an engine idle speed error, such idle speed error being representative of the difference between an idle speed set point and determined rotational speed, n.
In accordance of one feature of the invention, a method is provided for generating an idle control signal for an internal combustion engine. The method includes: determining rotational speed, n of the engine; estimating in-cylinder air charge; estimating combustion generated torque xcfx84ind as a function of the measured engine rotational speed, n, and the estimated cylinder air charge; and producing the idle control signal for the engine as a function of the difference between: (A) a time rate of change in such determined engine rotational speed, dn/dt, and; (B) the sum of the estimated combustion generated torque xcfx84ind and a function of an engine idle speed error, such idle speed error being representative of the difference between an idle speed set point and the determined rotational speed, n.
In accordance with another feature of the invention, a method is provided for generating an idle control signal for an internal combustion engine. The method includes: determining rotational speed, n of the engine; determining mass air flow through an intake manifold throttle of the engine; estimating cylinder air charge as a function the determined mass air flow; estimating combustion generated torque xcfx84ind as a function of the determined engine rotational speed, n, and the estimated cylinder air charge; and producing the idle control signal for the engine as a function of the difference between: (A) a time rate of change in such determined engine rotational speed, dn/dt, and; (B) the sum of the estimated combustion generated torque xcfx84ind and a function of an engine idle speed error, such idle speed error being representative of the difference between an idle speed set point and the determined rotational speed, n.
The current invention, may equivalently be performed in two steps. First, a real-time estimation of the engine losses and loading is obtained using an estimate of the current cylinder air charge (which may be estimated from measured mass airflow through the intake manifold) and a function of the change in engine speed. Then, the idle speed control is provided as the sum of the engine losses and loading, and a function of the idle speed error. It may be seen that this approach is equivalent to the previous embodiments. In this strategy, only the relationship between total, or net, engine torque and engine speed need be modeled and calibrated. Hence this value is readily available without additional sensors or calibration effort. The dependence on the change in engine speed is fundamentally related to the total inertia of the engine, and hence is not dependent on changes in environmental or driving conditions. Furthermore, this simple strategy requires no foreknowledge of the presence of a load (e.g., the air conditioner clutch engaging) and allows a reduction in the required vehicle sensor set.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.